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 * Copyright (c) 2013, SRI International
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 * Licensed under the The BSD 3-Clause License;
 * you may not use this file except in compliance with the License.
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 * 
 * http://opensource.org/licenses/BSD-3-Clause
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * Redistributions of source code must retain the above copyright
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package com.sri.ai.grinder.library.equality.formula.helper;

import java.util.ArrayList;
import java.util.List;

import com.google.common.annotations.Beta;
import com.sri.ai.expresso.api.Expression;
import com.sri.ai.grinder.api.RewritingProcess;
import com.sri.ai.grinder.core.AbstractRewriter;
import com.sri.ai.grinder.core.HasKind;
import com.sri.ai.grinder.library.FunctorConstants;
import com.sri.ai.grinder.library.boole.And;
import com.sri.ai.grinder.library.boole.Or;

/**
 * Distributes ors over ands in a formula: 
 *
 * F1 or (F2 and F3)  -> (F1 or F2) and (F1 or F3)
 * (F1 and F2) or F3  -> (F1 or F3) and (F2 or F3)
 * 
 */
@Beta
public class DistributeOrOverAnd extends AbstractRewriter {
	
	public DistributeOrOverAnd() {
		this.setReifiedTests(new HasKind(FunctorConstants.OR));
	}
	
	@Override
	public Expression rewriteAfterBookkeeping(Expression expression,
			RewritingProcess process) {
		Expression result = expression;
		
		if (expression.numberOfArguments() > 0) {
			// F1 or (F2 and F3) -> (F1 or F2) and (F1 or F3)
			// (F1 and F2) or F3 -> (F1 or F3) and (F2 or F3)
			for (Expression disjunct : expression.getArguments()) {
				if (And.isConjunction(disjunct) && disjunct.numberOfArguments() > 0) {
					List<Expression> otherDisjuncts = new ArrayList<Expression>(expression.getArguments());
					otherDisjuncts.remove(disjunct);
					
					List<Expression> conjuncts = new ArrayList<Expression>();
					for (Expression conjunct : disjunct.getArguments()) {
						ArrayList<Expression> disjuncts = new ArrayList<Expression>(otherDisjuncts);
						disjuncts.add(conjunct);
						conjuncts.add(Or.make(disjuncts));
					}
					result = And.make(conjuncts);
					break;
				}
			}
		}
		
		return result;
	}
}